As the only natural satellite of the Earth, the Moon is the brightest object in the night sky. Considerably smaller than Earth, the Moon is only about 27 percent the radius of Earth. Its mass is also much smaller, resulting in a relatively weak lunar gravity. The Moon is scarred by impact craters and has remained largely unchanged for billions of years. Today the Moon remains the only celestial body visited by man. NASA Apollo astronauts landed on the Moon six times, between 1969 and 1972. The Moon's orbit is moving away from Earth at a rate of 1.5 inches (3.8cm) a year.

A Lunar eclipse occurs when the Moon passes through the shadow of the earth. Since this happens when the Earth is directly between the Moon and the Sun, an eclipse occurs only when the Moon is full. Although the Earth is blocking the light of the Sun, the Moon does not darken completely during most lunar eclipses. The atmosphere of the Earth can bend part of the sun's light around the earth and toward the Moon. In some cases, it can have a faint reddish illumination.

See our other images for more on this subject and other formats of this video.